Abstract
The implementation of Software-Defined Networking (SDN) in Flying Ad-hoc Networks
(FANETs), known as SDN-FANET, has gained significant traction in the past decade.
This is particularly due to its eccentric capabilities and features which effectively
enhance the operation and performance of Unmanned Aerial Vehicles (UAVs) in various
applications. SDN-FANETs introduces adaptability and programmability to the network
by centralizing its control. A single entity known as the SDN controller, carries
out the network control's management and operation. However, this centralized approach
introduces a significant risk: a Single Point of Failure (SPoF) associated with the
SDN controller. The failure of the controller can lead to severe network disruptions.
Therefore, to tackle this challenge, recent research has focused on decentralizing
the SDN controller. This survey presents, compares, and analyzes the latest work done
in mitigating the centralization issue. Various approaches to decentralization, such
as multi-controller architectures, distributed control, and hybrid models, are discussed
based on their effectiveness in improving network scalability, reliability, energy
efficiency, routing, security, and cost of implementation. In addition, we categorized
these schemes in terms of the main technologies utilized: Cloud & Edge, Blockchain,
a hybrid of both, and miscellaneous ones. Our work also highlights important findings
from the discussed solutions, and open research issues in the context of SDNFANETs
along with some possible future directions. By identifying these research gaps, our
survey contributes to the understanding of future research directions in the field
of SDN-FANETs.